feat(17-01): richeditor field type on the seaglass sanitizer

- seaglass (new module): bluemonday v1.0.27 policy ported from Journal
  without the Blog Editor rules, byte-stable token comparison,
  SanitizeReport, Sanitize, Check, Removals
- cabana: type richeditor (common keys plus size); every create and update
  value sanitized before Fill, non-string values are a 422, removals become
  meta.notices; settings and relation forms refuse the type
- backend lang richeditor.removed_* and markup_changed (en, pl plurals)
- TestSeaglassSmoke, TestCompanionsRichEditorSmoke, README and docs

modules/cabana/testdata/companions/models/link/fields.yaml

@@ -12,3 +12,7 @@ fields:
         type: dropdown
         dependsOn: type
         emptyOption: backend::lang.form.none
+    description:
+        label: Description
+        type: richeditor
+        size: large